Potterton E110 Fault Code: Causes, Fixes & Repair Costs
What does the Potterton E110 fault code mean?
The E110 code appears on your Potterton boiler when the internal safety thermostat has tripped because the boiler reached an unsafe temperature. Rather than continuing to run and risk damage or danger, the boiler shuts itself down as a protective measure. You will lose both heating and hot water, and you may hear banging or gurgling from the system. Potterton shares its fault code system with Baxi and Main boilers — all three brands are under the same parent company and use identical codes, so E110 means exactly the same thing and is diagnosed in exactly the same way across all three ranges.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Low system pressure Common
When the system pressure drops below around 1 bar the boiler cannot circulate water effectively, heat builds up rapidly and the overheat thermostat trips. This is one of the most frequent triggers for E110 and is worth checking first. A cold-system reading between 1.0 and 1.5 bar is normal.
- Circulation pump failure or seizure Common
The pump is responsible for moving heated water around the system. If it seizes, runs slowly, or fails entirely, water sits in the heat exchanger and overheats. A failing pump may make a humming or grinding noise, or feel unusually hot to the touch.
- Blocked or scaled heat exchanger Common
Over time, limescale in hard-water areas and iron oxide sludge from the system can build up inside the heat exchanger, restricting water flow. Heat cannot be carried away from the burner efficiently, causing temperatures to rise until the safety thermostat trips.
- Trapped air or airlock Sometimes
Air pockets in the system or within the boiler itself interrupt water flow, creating localised hot spots. This often accompanies gurgling or banging sounds and can appear after radiator work, a pressure loss, or a system top-up.
- Faulty overheat thermostat or temperature sensor Sometimes
If the safety thermostat or an NTC temperature sensor has developed a fault, it may either trip unnecessarily at normal operating temperatures or fail to provide accurate readings — either way the boiler logs E110 and shuts down.
- Blocked flue or restricted air supply Sometimes
A partially blocked flue or air inlet can affect combustion efficiency. In some circumstances this contributes to overheating by disrupting the normal operating cycle of the burner.
- Frozen or blocked condensate pipe Sometimes
During cold spells the plastic condensate pipe that runs externally can freeze solid, causing the boiler to lock out. While primarily triggering a condensate-specific code, a prolonged blockage can contribute to overheating conditions in some Potterton models.
- Faulty gas valve Rare
A gas valve that is not modulating correctly can cause the burner to run hotter than intended, triggering the safety thermostat. This is a less common cause but is considered when other components check out fine.
How to fix it
- Let the boiler cool down completely before attempting anything DIY safe
Switch the boiler off at the programmer or thermostat and leave it for at least 10–15 minutes. The safety thermostat must cool before a reset will hold. Attempting a reset on a still-hot boiler usually results in an immediate re-lockout.
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the front of the boiler. With the system cold it should read between 1.0 and 1.5 bar. If it is below 1 bar, use the filling loop (usually a braided hose beneath the boiler with one or two valves) to slowly top the pressure up to around 1.2–1.3 bar, then close the filling-loop valves fully.
- Bleed any radiators that feel cool at the top DIY safe
Use a radiator bleed key to release trapped air from any radiators that are not heating evenly. Start on the ground floor and work upward. Once water (not air) trickles from the bleed valve, close it. Recheck the system pressure afterwards and top up again if it has dropped below 1 bar.
- Check whether the condensate pipe is frozen (winter months only) DIY safe
Find the white plastic condensate pipe that exits the boiler and runs to an outside drain. If it feels solid or has visible ice around it, carefully pour warm (not boiling) water along its length to thaw it. Repeat until the blockage clears. Never use a naked flame.
- Attempt a boiler reset DIY safe
Once the boiler has cooled, pressure is correct, and any obvious issues have been addressed, press and hold the reset button for approximately 5 seconds as described in the Potterton manual. Do not reset the boiler more than two or three times — repeated resets without resolving the root cause can cause internal damage. If the E110 code returns promptly after resetting, stop and call an engineer.
- Have a Gas Safe engineer inspect the circulation pump Gas Safe engineer
If the fault persists, a qualified engineer should test the pump for correct operation, speed, and flow rate. A failed or seized pump is one of the most common causes of E110 and usually requires replacement — a Grundfos or equivalent quality pump fitted by an engineer typically costs around £200–£280 all in.
- Have a Gas Safe engineer assess the heat exchanger for sludge or scale Gas Safe engineer
An engineer can check water flow rates and inspect for signs of scale or magnetite sludge. If the system is heavily contaminated, a power flush is often recommended before or alongside any component replacement. Adding a magnetic filter during this process helps prevent recurrence.
- Have a Gas Safe engineer test the thermostats, temperature sensors, and gas valve Gas Safe engineer
Faulty overheat thermostats, NTC sensors, or a misbehaving gas valve all require gas-registered, trained diagnostics and replacement. The engineer will use a flue-gas analyser and test equipment to pinpoint the exact component at fault.
- Call a Gas Safe registered engineer if the fault has not cleared Gas Safe engineer
If you have worked through the homeowner checks above and the E110 code continues to appear, do not keep resetting the boiler. Contact a Gas Safe registered engineer to carry out a full boiler inspection. You can verify an engineer's registration at gassaferegister.co.uk.
Parts you may need
- Circulation pump (e.g. Grundfos UPS2 or equivalent) · from £80
- Overheat safety thermostat · from £25
- NTC temperature sensor (flow or return) · from £20
- Printed circuit board (PCB) · from £180
- Magnetic system filter (e.g. Fernox TF1 or Magnaclean) · from £60
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£380, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting the boiler to clear the E110 code?
It is tempting, but you should not. The E110 code means the boiler overheated and tripped a safety device. Running the boiler again without addressing the underlying cause risks damaging internal components — particularly the heat exchanger — which can turn a relatively inexpensive repair into a far more costly one. Limit yourself to two or three resets maximum, and only after you have checked system pressure and let the boiler cool fully.
How much does it typically cost to fix a Potterton E110 fault in the UK?
For the most common causes, most homeowners pay somewhere between £150 and £380. A pump replacement including labour generally comes in around £220–£280. Thermostat or sensor replacements are usually cheaper, often £120–£180 all in. A power flush to clear sludge typically costs £300–£500 depending on the number of radiators. Heat exchanger replacement is a larger job — costs can reach £400–£600 or more — and on older boilers (10–12 years plus) it is often more economical to replace the boiler entirely.
Is the Potterton E110 the same fault as on a Baxi or Main boiler?
Yes, exactly the same. Potterton, Baxi, and Main are all owned by the same manufacturer and share an identical control and fault-code system. An E110 on any of these three brands means the safety thermostat has operated due to overheating, and the diagnosis and repair process is identical across all three.
What can I do to prevent the E110 fault from coming back?
Book an annual boiler service with a Gas Safe engineer — this is the single most effective step. During a service the engineer will check system pressure, inspect the pump, clean the burner, test sensors, and flag early signs of sludge or scale. If your system does not already have one, fitting a magnetic filter (such as a Fernox TF1 or Adey Magnaclean) will capture iron oxide sludge before it can accumulate in the heat exchanger. In hard-water areas, scale inhibitor added to the system water also helps.